The invention of this application is related to that of our copending application entitled "Inspection method using unique template and histogram analysis", Ser. No. 07/706,800, Filed May 29, 1991 now U.S. Pat. No. 5,204,911.
Background--Field Of The Invention
Generally, the field of this invention relates to quality control, particularly to a machine for inspecting and measuring products moving on a production line. The products are accepted for use or rejected based up on the inspection results.
Background--Prior Art
Image processing systems are used a great deal in today's product quality control systems. Image processing systems are replacing human power since they have the advantages of higher throughput, better inspection accuracy and lower cost.
An inspection system contains a light source with a unique wavelength that illuminates the product being inspected. Images of the products inspected are stored in a computer's memory for analysis by means of an algorithm, which is also stored in the computer's memory.
Recently, the structure of products has became more complicated and harder to inspect. A preformed product 102 (FIG. 1) is the first stage of a full-sized plastic container. The ovality, that is the roundness of the preform, is measured in one inspection operation before the product is inserted into a glass or plastic blowing machine (not shown), in which it is expanded into a full-sized container.
The ovality measurement must be very accurate. If a preform's ovality is not within the desired accuracy, it must be rejected before entering the blowing machine. If an inferior preform does get into the blowing machine, it will break, causing damage to the machine and stopping the production line.
Another common inspection operation on a production line (after the preform is blown into a container, filled, and sealed or capped) is to detect the seal or cap on the top of a container. The position of the seal must be very accurate to prevent gas or liquid from leaking out of the container.
Today high speed, very accurate, and cost effective inspect-on machines are needed. An automated inspection machine analyzes images of complicated structures, such as preforms 102 (FIG. 1) and seats (caps) 204 (FIG. 2) which are positioned on the product. The images are taken by a video camera and stored in the memory of a computer. Several standards for image acquisition exist, depending on the type of the camera used. In the US the standard is known as RS170 which generates an image of 491 horizontal lines by 649 pixels per line. The acquisition rate is 3 images per second. There are non-standard cameras with higher rates of image acquisition, or line cameras that use line sensors with various numbers of pixels.
Complicated measurements of highly structured products, such as containers, need a line-by-line image algorithmic analysis. That requires a lot of processing time and results in low production line throughput.